New post gives "You are currently editing the page that shows your latest posts.

Hi, when I go to any site in my multisite and add new post I get only the post title field and then a banner that says:

“You are currently editing the page that shows your latest posts.”

I’m trying to find out what recent changes, if any, were made, and I’ve tried disabling all plugins. I’ve also tried making a backup of the site (with Updraft) or reinstalling WP, but nothing happens when I do either of those, if that’s useful as a diagnostic.